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Different brain wave frequencies, called bandwidths, relate to different mental states. They are named after letters of the Greek alphabet. Neurofeedback therapy is used to reduce or increase specific brainwave frequencies depending on the problem.
Delta is the slowest frequency of brain wave activity. Frequency is a measurement of the oscillations, or the cycles per second, of the brain waves. This electrical activity is hypothesized to emerge from vast aggregates of neurons as they communicate and process information. The source of this activity is considered to be the postsynaptic changes in electrical potential along the membrane of the dendrites. Delta is the slowest brain wave and is measured from .5 to about 4 cycles per second. Delta is only seen in the adult EEG in the deep sleep state that occurs within the first two hours of the sleep cycle. If it is seen in the waking state in an adult, it could indicate some type of abnormality.
The next brainwave bandwidth is Theta. Theta occurs between 4 and 8 cycles per second. Theta in the adult EEG can indicate drowsiness, it-can also indicate some abnormalities. Sometimes people with head injuries will show excessive Theta activity either at the sight of the injury or other areas of the brain. Theta has also been found to be outside the norm in some children with ADD and ADHD and sometimes in children with learning disabilities.
The next bandwidth is Alpha. The mental state of Alpha is similar to putting the clutch in before shifting the gears; it is just sort of a holding pattern. Approximately Ninety-five percent of the population has a peak Alpha frequency with eyes closed and that is considered very normal. Alpha predominance essentially represents a brain that is quiet and at rest. An important point is that Alpha ranges from 8 to 12 cycles per second. There is some research that shows a difference in the mental activity of; let's say, 8 cycles per second Alpha and 12 cycles per second Alpha. In other words, you can do some focused thinking at 12 cycles per second Alpha, that you can't do at 8 cycles per second Alpha. We are finding that the bandwidths are actually very broad and are used to identify the morphology, that is, the shape of the waves. Specific frequencies within those bandwidths may correlate with slightly different mental activity.
Beta is anywhere from 13 cycles per second all the way on up to over 32 cycles per second. This is where things get very interesting. Low frequency Beta, between 13 and 15 cycles per second, has also been referred to as "sensory motor rhythm" and it seems to be a very important rhythm. It has the ability to organize the brain in terms of biofeedback. It is being used for ADD and learning disabilities, as well as a variety of emotional problems, and for peak performance models. It has to do with the coordination of many areas of the brain. By teaching an area of the brain to make more low frequency Beta activity, it actually effects many pathways within the brain in many different ways. We use it often for sleep disorders. From 15 hertz on up, we speed up in frequency so the brain becomes more focused, more concentrated ... up to about 20 hertz. From 20 hertz on, too much Beta activity can backfire. What starts to happen is that there is too much activity, too much electrical noise occurring in the brain. You actually see functioning, organizational and concentration abilities start to deteriorate from there on. However, some researchers are now looking at extremely high frequencies of Beta... going from the 100 cycle per second range, all the way up to the 120-hertz range in specific areas of the brain... primarily the temporal areas, which are on the sides of the head. They are looking at those frequencies because they suspect there is a correlation between those very high frequencies and psychic abilities, as well as advanced levels of meditation where the meditator experiences a dramatic shift in consciousness known as transcendence.